I1O HENRY SHALER WILLIAMS 
ton, the horizon is (recognized as) in the Ithaca member of the Nunda; 
when the Delthyris is associated with them, but below the place of 
first appearance of the diagnostic Chemung species, the horizon is 
upper Nunda: i. e., the Van Etten zone of Tropidoleptus. Still later, 
after the Chemung species were upon the ground, in the lower part 
of the zone of Dalmanella tioga, Tropidoleptus again occurs. It is 
this third stage of its recurrence that was referred to in the list of species 
given on p. 24, of Bulletin No. 3 of the U. S. Geological Survey. It 
was numbered A® + and called ‘the second recurrence of the Tropido- 
leptus stage” in my paper on the classification of the Upper Devonian 
in 1886." 
The line thus determined as the horizontal boundary between the 
Nunda and the Chemung is traceable eastward as well as westward, 
by the range of the fossils which furnish a definite paleontologic means 
of discriminating the Chemung formation throughout its geographic 
extent. 
The references to Dalmanella in Contributions to Devonian Pale- 
ontology of 1903? have been re-examined critically in the light of 
these investigations. All the citations of Dalmanella tioga and D. 
carinata are correct and the horizons containing them are unmis- 
takably Chemung. The reference to the species Dalmanella tenuilin- 
eaia, on p. 33 faunule 1379B, is based on a single specimen, and the 
species is the one described by Hall under the name Orthis leonensis. 
The specimens identified, on pp. 36 and 37, as Dalmanella tenui- 
lineata (from faunules 1380B° and B7) are in both cases associated 
with Spirijer disjunctus leaving no doubt as to the horizon, but they 
are specimens of a small Schizophoria and should not be referred 
to the genus Dalmanella. The specimen identified as Dalmanella 
in faunule 1453A3 on p. 70, does not exhibit the characteristic features 
of Dalmanella. 
In using the faunal method of determining the boundary line 
between the Nunda and Chemung the assumption is made that a 
faunal distinction was applicable to the Chemung group as originally 
defined by Hall. This assumption is borne out by the later experi- 
ence of paleontologists in finding distinct evidence of this fauna in 
t Proc. A. A. A. Soc., Vol. XXXIV (1885), p. 226. 
2U. S. Geol. Survey, Bull. 244 (1905). 
oe 
